Preparation of highly efficient thermoelectric Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials with a scalable mechanical alloying method

Mg2Si-type compounds are highly promising materials for use in thermoelectric devices for waste heat energy harvesting. These compounds have great potential because they exhibit high thermoelectric performance, but the scalability of their synthesis is a major issue for applications. In this study, Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials were prepared by mechanical alloying combined with hot press sintering in order to increase the mass capabilities of their synthetic route compared with the typical solid state reaction. The optimum thermoelectric properties were achieved for the best Mg2Si0.57Sn0.4Bi0.03 and Mg2Si0.53Sn0.4Ge0.05Bi0.02 compositions by ball milling for 32 h and the maximum figure of merit (ZT) values were 1.07 and 1.2, respectively

Synthesis, characterization and thermoelectric performance of Mg2 (Si, Sn, Ge) materials using Si-kerf waste from photovoltaic technology

The recycling acquisition of silicon waste from photovoltaic industry has gained an increasing attention nowadays, since more than 50% of high purity material ends up as kerf during the wafer cutting process. Currently, different Si-based applications are being exploited in terms of using such Si kerf, in order to lower cost and significantly increase environmental impact. Thermoelectric devices can efficiently contribute towards this recycling approach, via the preparation of highly efficient silicides for power generation. In this work, Bi doped Mg2(Si,Sn,Ge) materials were prepared using Si-kerf originated from photovoltaic (PV) cutting wastes. Different Bi concentrations were studied in terms of thermoelectric properties and performance and a high figure-of-merit of 1.1. was achieved at 800K. In addition, a thorough structural and mechanical property characterization, such as morphology, phase identification, hardness and indentation modulus has been conducted. These results, which were evaluated and compared to materials prepared with pure Si (>99.9%), are presented for the first time for Mg2(Si,Sn,Ge) materials

Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO₂/TiO₂ Thin Films

Controlling the semiconductor-to-metal transition temperature in epitaxial VO₂ thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO₂ epitaxial thin films grown on TiO₂ substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V⁴⁺–V⁴⁺ bond direction, the crystallographic <i>c</i>-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO₂/TiO₂ multilayer structures